The present invention relates to semiconductor design technology; and, more particularly, to a semiconductor memory device capable of controlling a driving force of a high voltage in consideration of a PVT (Process, Voltage, Temperature) fluctuation.
Generally, a high voltage generator is an apparatus for supplying a constant level of a high voltage to a circuit in a chip which needs an increased voltage (hereinafter, referred to as ‘VPP’ higher than a power supply voltage (VDD or VCC). Particularly, the high voltage generator has been used for a word line driver, a bit line gating circuit and a data output buffer in the memory device such as a DRAM (Dynamic Random Access Memory).
FIG. 1 is a block diagram of a high voltage generator according to a conventional semiconductor memory device, wherein the high voltage generator generates a high voltage (VPP) which is higher than an external voltage (VDD).
Referring to FIG. 1, the high voltage generator according to the conventional semiconductor memory device includes a level detecting unit 22, a standby VPP generating unit 24, first to fourth banks 12, 14, 16 and 18, an active control signal generating unit 30 and first to fourth active VPP generating units 42, 44, 46 and 48. The level detecting unit 22 detects a high voltage (VPP) and then produces a high voltage driving signal VPP_ST_EN. The standby VPP generating unit 24 produces the high voltage (VPP) having a voltage level higher than an external voltage (VDD) in response to the high voltage driving signal VPP_ST_EN. Each of the first to fourth banks 12, 14, 16 and 18 stores data and reads out them in response to a corresponding bank driving signal BK_ACT0, BK_ACT1, BK_ACT2 or BK_ACT3. The active control signal generating unit 30 receives a plurality of bank driving signals BK_ACT0, BK_ACT1, BK_ACT2 and BK_ACT3 and the high voltage driving signal VPP_ST_EN and then produces a plurality of high voltage active driving signals VPP_ACT_EN_0, VPP_ACT_EN_1, VPP_ACT_EN_2 and VPP_ACT_EN_3. Each of the first to fourth active VPP generating units 42, 44, 46 and 48 produces the high voltage in response to the corresponding high voltage active driving signal VPP_ACT_EN_0, VPP_ACT_EN_1, VPP_ACT_EN_2 or VPP_ACT_EN_3.
The active control signal generating unit 30 includes first to fourth active control signal generating units 32, 34, 36 and 38. The first active control signal generating unit 32 produces the first high voltage active driving signal VPP_ACT_EN_0 in response to the first bank driving signal BK_ACT0 of the first bank 12 and an activation of the high voltage driving signal VPP_ST_EN. The second active control signal generating unit 34 produces the second high voltage active driving signal VPP_ACT_EN_1 in response to the second bank driving signal BK_ACT1 of the second bank 14 and the activation of the high voltage driving signal VPP_ST_EN. The third active control signal generating unit 36 produces the third high voltage active driving signal VPP_ACT_EN_2 in response to the third bank driving signal BK_ACT2 of the third bank 16 and the activation of the high voltage driving signal VPP_ST_EN. Finally, the fourth active control signal generating unit 38 produces the fourth high voltage active driving signal VPP_ACT_EN_3 in response to the fourth bank driving signal BK_ACT3 of the fourth bank 18 and the activation of the high voltage driving signal VPP_ST_EN.
For reference, the first to fourth active VPP generating units 42, 44, 46 and 48 are respectively arranged in the vicinity of the first to fourth banks 12, 14, 16 and 18 so that each of the first to fourth active VPP generating units 42, 44, 46 and 48 produces the corresponding high voltage (VPP) when the corresponding bank is activated.
The operation of the high voltage generator according to the conventional semiconductor memory device of FIG. 1 will be described below.
First, the level detecting unit 22 decides whether the high voltage (VPP) undergoes a voltage drop to a level below a reference level and activates the high voltage driving signal VPP_ST_EN. Subsequently, the standby VPP generating unit 24 is activated by the high voltage driving signal VPP_ST_EN. The activated standby VPP generating unit 24 conducts an operation for charge-pumping the external voltage (VDD) in order to produce the high voltage (VPP) so that the high voltage (VPP) is maintained in the reference level.
Moreover, if the corresponding bank driving signal BK_ACT0, BK_ACT1, BK_ACT2 or BK_ACT3 is activated during the activation of the high voltage signal VPP_ST_EN, the active control signal generating unit 30 activates the corresponding high voltage active driving signal VPP_ACT_EN_0, VPP_ACT_EN_1, VPP_ACT_EN_2 or VPP_ACT_EN_3 in response to the activation of the corresponding bank driving signal BK_ACT0, BK_ACT1, BK_ACT2 or BK_ACT3. Subsequently, the first to fourth active VPP generating units 42, 44, 46 and 48 are additionally activated in response to the corresponding high voltage active driving signal VPP_ACT_EN_0, VPP_ACT_EN_1, VPP_ACT_EN_2 and VPP_ACT_EN_3, thereby supplying the high voltage (VPP).
The reason why the first to fourth active VPP generating units 42, 44, 46 and 48 are additionally activated is that it is necessary to stably maintain the level of the high voltage (VPP) in consideration of the consumption of the high voltage (VPP) which is caused by the activated bank in an active mode.
That is, when the high voltage (VPP) undergoes the voltage drop and is below the reference level, the conventional semiconductor memory device supplies the high voltage (VPP) by driving the standby VPP generating unit 24 and additionally drives the first to fourth active VPP generating units 42, 44, 46 and 48 in an active mode where the bank is accessed.
On the other hand, the reason why the high voltage generating units for supplying the high voltage (VPP) are classified into the standby mode and the active mode as described above is that an amount of power consumption of the high voltage (VPP) in the standby mode is different from that in the active mode. That is, in order to achieve the reduction of the power consumption and the implementation area, the drivability of the high voltage generating units is controlled according to the amount to be required in each mode. More specifically, since the high voltage (VPP) is little used in the standby mode, the standby VPP generating unit 24 which is activated in this mode can maintain the required voltage level even though the standby VPP generating unit 24 does not have a large drivability. However, since the usage of the high voltage (VPP) is increased in the active mode, the required voltage level is maintained by driving the additional active VPP generating units 42, 44, 46 and 48.
Therefore, it is important to design the semiconductor device so that the standby VPP generating unit 24 and the active VPP generating units 42, 44, 46 and 48 satisfy the required level of the high voltage (VPP) according to the established mode. However, even though the design is set up to control the drivability of the high voltage generating unit, an excessive or insufficient amount of the voltage level can be caused by the amount of the supplied external voltage (VDD) in the actual operation. With respect to this problem, the detailed operation will be described below referring to FIG. 2.
FIG. 2 is a graph showing a variation of the high voltage (VPP) in the standby mode and the active mode according to the external voltage (VDD). For reference, ‘a’ expressed by the solid line shows the level of the high voltage (VPP) in the standby mode and ‘b’ expressed by the dotted line shows the level of the high voltage (VPP) in the active mode.
As shown in FIG. 2, the high voltage (VPP) is generated when the level of the external voltage (VDD) is secured over a predetermined value. After the external voltage (VDD) is secured, the level of the high voltage (VPP) is kept in a stable level regardless of the increase of the external voltage (VDD) along the solid line ‘a’.
However, in the case of the dotted line ‘b’, when the level of the external voltage (VDD) is low, the high voltage (VPP) is supplied in the relatively low level, as compared with that in the case of the solid line ‘a’. Also, in the case of ‘b’, when the level of the external voltage (VDD) is high, the high voltage (VPP) is supplied in the relatively high level, as compared with that in the case of the solid line ‘a’. That is, it is seen that level ‘b’ of the high voltage (VPP) in the active mode is affected by the amount of the supplied external voltage (VDD) and then is not maintained in a stable voltage level.
In order words, the level of the high voltage (VPP) is very much affected by the external voltage (VDD) in the active mode, as compared with that in the standby mode.
More specifically, the standby VPP generating unit 24 supplies the high voltage (VPP) higher than the external voltage (VDD) by charge-pumping the external voltage (VDD). However, although the standby VPP generating unit 24 has a driving force, the amount of the supplied high voltage (VPP) that is provided by the standby VPP generating unit 24 is also small regardless of the driving force of the standby VPP generating unit 24 in the case where the amount of the supplied external voltage (VDD) is relatively small. Moreover, in the case where the level of the external voltage (VDD) is high and the amount of the supplied external voltage (VDD) increases, the amount of the supplied high voltage (VPP) which is provided by the standby VPP generating unit 24 may become greater.
However, as illustrated above, since the power consumption of the high voltage (VPP) is small in the standby mode, the level of the high voltage (VPP) can be stably maintained even if the amount of the supplied high voltage (VPP) is reduced due to the low amount of the external voltage (VDD).
On the other hand, since the power consumption of the high voltage is much greater in the active mode, the amount of the high voltage (VPP) is also reduced, when the high voltage (VPP) is caused by the low level of the external voltage (VDD), and this reduced high voltage can not satisfy the required power supply to make a normal operation achieved in the circuit. In the active mode, if the external voltage (VDD) has a high level, the supplied amount of the high voltage (VPP) is also increased and the increased high voltage (VPP) is over the required amount for normal circuit operation.
Therefore, to solve this problem, if the driving force of the active VPP generating unit is increased based on the low level of the external voltage (VDD), the insufficient amount of the high voltage (VPP) can be compensated. However, when the external voltage (VDD) is increased, the high voltage (VPP) may be excessive.
Therefore, in the active mode, the high voltage (VPP) is affected by the level of the external voltage (VDD) so that the high voltage (VPP) is unable to be adequately supplied and is below the reference level or is excessively supplied over the reference level. As a result, the conventional high voltage generating unit has a problem in that the reference level is not maintained stably.
As described above, the phenomenon that the level of the high voltage is unable to be stably maintained by the level of the external voltage can be caused by the ambient temperature, at the time of driving the VPP generating unit, or the manufacturing process of the semiconductor memory device. For example, even though the level of the external voltage is kept stable, the driving force of the VPP generating unit may be increased or decreased by the ambient temperature or the processing of the semiconductor device. In the standby mode, the high voltage can be supplied to an internal circuit regardless of the variation of the driving force because the power consumption is relatively small; however, in the active mode, the reduction of the driving force decrease the level of the high voltage and the increase of the driving force makes the level of the high voltage increased, because the power consumption of the high voltage is much more.
The high voltage generating unit according to the conventional semiconductor device supplies the high voltage insufficiently or excessively in compliance with the external voltage, the processing procedures and the variation of the ambient temperature. Therefore, the reliability of the device is decreased due to the data failure and the yield of the device is also decreased because the high voltage is not provided appropriately to the internal circuit of the device.